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http://www.atmosedu.com/Geol390/articles/RoyeretalCO2GSAToday%2704PhanerozoicClimate.pdf CO2 has been a driver of Climate for Millions of years. (phanerozoic 550 Mya to present) There have been large ice sheets during the Phanerozoic ~300 Mya Our present Ice age began around 2 MYa